What is the UY85 vacuum tube?

The UY85 (UY85 / 38A3) is a rectifier vacuum tube designed for rectifier applications. Series-heater half-wave rectifier..

What is a UY85 substitute or equivalent?

Direct equivalents to the UY85 include 38A3, U381. These share the same pinout and operating envelope, so they can usually be swapped without circuit changes — though batch-to-batch variations between manufacturers (NOS vs current production) may shift the sonic character noticeably.

Is the UY85 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the UY85 as Common availability. NOS (new-old-stock) examples from RCA, Mullard, Tung-Sol, GE, Sylvania and Telefunken trade among collectors; modern production where it exists comes mostly from JJ Electronic, Electro-Harmonix, Tung-Sol (New Sensor), Genalex, and a handful of small-batch makers.

What does the UY85 sound like?

Series-heater half-wave rectifier.. Sonic character also depends heavily on the circuit operating point, the surrounding tubes in the stage, and the output transformer when present — use the interactive loadline calculator on this page to explore the trade-offs.

UY85 38A3 Rectifier Vacuum Tube

Also known as 38A3 · U381

Full-wave rectifier for vacuum tube power supply designs

RectifierHeater 38 V · 0.1 A9-pin NovalMullard·Philips 1955

Max DC output current: 110mA
Peak inverse voltage: 700V
Max RMS input per anode: 250V
Peak anode current: 660mA

UY85

Characteristics

Datasheet values, once each. Every value cites its sheet.

HeaterIndirectly heated

Specifications of UY85 — Heater
Heater voltageVh	38 V
Heater currentIh	0.1 A

Rectifier limitsDatasheet maximum ratings — not to be exceeded

Specifications of UY85 — Rectifier limits
Max RMS input voltage per anode	250 V
Io max (DC output current)	110 mA
Peak inverse voltage (PIV)	700 V
Peak anode current	660 mA
Max reservoir capacitor	100 µF
Min series resistance per anode	100 Ω

Mechanical

Specifications of UY85 — Mechanical
Base	9-pin Noval
Rarity	Common
Pinout

datasheet cited · model or editorial reading · catalogue value, no citation attached yet · nothing invented

Using this tube

Interactive loadline calculator not available for this tube yet — it needs calibrated Koren or Ayumi parameters.

Applications

Power supply rectification

Generic rectifier rectifier stage

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026

Manufacturer datasheets

6 manufacturer datasheets cross-checked for UY85 / 38A36 verified

UY85 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: Mullard·Philips
Reviewed: 2026-05-29
Status: DataModelCalc
Model: under review

Context

The UY85 is a indirectly-heated rectifier from Mullard·Philips, introduced around 1955. Commonly used in rectifier applications. Series-heater half-wave rectifier.

History

Introduced: 1955
Manufacturer: Mullard·Philips
Era: Golden Age

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